The present invention, in some embodiments thereof, relates to a conditional MO-1 knock-out non-human animal and, more particularly, but not exclusively, to methods of generating and using same.
Obesity stems from a prolonged imbalance between the levels of energy intake and expenditure, with the resultant surplus being stored as body lipids. Our understanding of the regulation of food intake and the physiological basis of differences in energy expenditure is owed, in large part, to studies made in animals. Moreover, animal models have been a cornerstone of studies of environmental effects, such as epigenetics, responses to high-fat and low-calorie diets and the identification and development of pharmaceuticals for obesity treatment
Obesity is a major risk factor for type II diabetes mellitus, heart disease, hypertension, metabolic syndrome, and cancer and is increasingly prevalent in Western society and in developing countries. Today, more than 1.1 billion individuals are overweight and more than 300 million are obese. Obesity is assessed by the calculation of the body mass index (BMI) [weight/(height)2 in kg/m2]. Individuals with a BMI higher or equal to 30 kg/m2 are considered obese, whereas those with a BMI higher than 40 are morbidly obese. Despite intense scrutiny of this worldwide public health problem, the molecular and regulatory mechanisms which underlie the differences between lean and obese individuals remain largely unknown. Obtaining a better understanding of how energy balance is controlled should provide the framework for future clinical intervention and rational drug design.
In humans, the importance of genetic factors in obesity has been clearly defined through numerous twin, familial aggregation, and adoption studies. Indeed, through these studies heritability has been estimated as high as 40-90%. In the absence of rational gene candidates, genome-wide genetic association studies have emerged as a potentially powerful tool, and, as may be predicted, numerous genome-wide linkage studies have identified novel candidate gene loci for future studies. Unfortunately, these linkage studies have generally identified broad chromosomal regions containing scores of candidate genes and expressed sequence tags (ESTs). Two major problems now exist. First, the large number of genes within these regions need to be individually characterized and second, biologically plausible gene candidates within these regions are not always intuitively obvious: obesity-related genes may regulate a broad spectrum of physiologic pathways, including those governing satiety, basal metabolic rate, and activity. In addition, novel genes or those unrelated to the present, limited understanding of disease pathophysiology may go undetected.
Most striking with regard to the genetic basis of obesity and providing insights into its molecular basis has been the identification of gene mutations causing a number of Mendelian obesity disorders. These include leptin and leptin receptor deficiencies, melanocortin 4 receptor and POMC deficiencies and the pleiotropic syndromes Prader-Willi and Bardet-Biedl. Unfortunately, while each have provided insight into the molecular basis by which the hypothalamus controls satiety and energy homeostasis, none has provided insight into more common forms of obesity nor has yet provided a useful drug target for obesity and its comorbid features including diabetes.
An enormous number of transgenic models with obese or lean phenotypes have been created since the characterization of the first obesity genes. Of particular interest are mutations discovered in the peptide hormone, leptin, which is a component of a novel signal transduction pathway that regulates body weight [Zhang Y et al., Nature (1994) 372: 425-432; Chen H et al., Cell. (1996) 84(3):491-5]. Leptin was initially discovered by the positional cloning of the obesity gene, ob, in mice. Two different ob alleles have been identified: one mutation causes the premature termination of the leptin peptide resulting in a truncated protein, and the other mutation changes the transcriptional activity of the obesity (ob) gene, resulting in a reduced amount of circulating leptin. The genetically obese ob/ob mouse is a classic case of a spontaneous single-gene loss-of-function mutation that generates massive obesity.
The 2005 update of the human obesity gene map cited 248 genes that, when mutated or expressed as transgenes in mice, result in phenotypes that affect body weight and adiposity [Rankinen T et al., Obesity (2006) 14: 529-644]. Current sophisticated gene-targeting strategies enable investigators to manipulate the genome in ways that allow introduction of virtually any desired change. Furthermore, advanced techniques allow genome alterations that act at specific times only or that are expressed in specific tissues or cell types.
Knock-out mice also play an important role in the prospective identification of putative pharmaceutical targets for drug development. For example, Powell reviewed the phenotypes of 21 different types of knock-out mice where the gene knocked out was a potential therapeutic target for obesity. He found that, where data were available, the knock-out phenotypes mimicked not only the effects of therapeutics in rodents, but also the effects when relevant therapeutics targeting the same genes were delivered to humans. Transgenic mouse technology may therefore be a valuable tool to prospectively identify genes that regulate body fat in vivo, and then to develop anti-obesity therapeutics by targeting the human protein products of these genes or by interfering with levels of fat storage [Powell D R. Obes Rev (2006) 7: 89-108].
The development of the cannabinoid receptor type 1 antagonist rimonabant, is an example of a drug target that was identified in animals, led to the development of a class of potential obesity therapeutics and which ultimately generated a useable drug [Powell, supra; Speakman J et al., Obesity Reviews (2007) 8 (s1): 55-61].
U.S. Patent Application No. 2010/0077496 relates to the isolated MO-1 nucleic acids, MO-1 polypeptides, oligonucleotides that hybridize to MO-1 nucleic adds, vectors, including expression vectors, comprising MO-1 nucleic acids, as well as isolated host cells, antibodies, transgenic non-human animals, compositions, and kits relating to MO-1. Methods of detecting the presence of MO-1 nucleic acid, screening for agents which affect MO-1 activity, and screening for MO-1 variants are also disclosed therein.
Additional background art includes U.S. Pat. No. 7,446,239, U.S. Patent Application No. 2010/0143934, U.S. Patent Application No. 2005/0158310 and PCT application No. WO 2000/066721.